1. Field of the Invention
The present invention relates to a speaker apparatus that is provided with a bass reflex structure.
Priority is claimed on Japanese Patent Application No. 2008-082512, filed Mar. 27, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
As a speaker apparatus that performs bass enhancement disclosed in Japanese Unexamined Patent Application, First Publication No. 2008-48176, a phase inversion-type enclosure is used. A phase inversion-type enclosure includes a speaker unit that is installed in a baffle plate that serves as a front panel of the cabinet, and a bass reflex port. The bass reflex port has an opening portion that is formed in the front panel of the cabinet and a cylindrical portion that is installed inside of the enclosure and connected to this opening portion.
A structure of a bass reflex port has been prepared to solve various issues.
For example, when the diameter of the bass reflex port is constant and an edge portion (angle portion) is at the end surface of its opening end, noise is produced by the generation of a vortex at the angle portion during air intake. In order to solve this issue, a structure is generally used that adds roundness in a radial shape to the angle of the opening ends 101′, 102′ of the bass reflex port 10′ as shown in FIG. 10. FIG. 10 shows the various structures of a general phase inversion-type enclosure 2′ in a conventional small-diameter speaker 1′.
The bass reflex port enhances the bass by employing the Helmholtz resonance that occurs due to an air spring inside of an enclosure and the air mass in the bass reflex port. Accordingly, the set frequency of the bass to be boosted is determined by the relationship between the shape of the cabinet 11′ that forms the enclosure 2′ and the shape of the bass reflex port 10′. For this reason, the inner diameter of the bass reflex portion 10′ may become small depending on the shape of the cabinet 11′.
When the inner diameter of the bass reflex portion 10′ becomes small, the flow velocity of air in the bass reflex port 10′ speeds up, and the discharge flow velocity from the port also speeds up. For this reason, in the case of a grill or punching metal being installed at the opening portion, the discharge air from the port collides with the grill or the like, producing noise. In order to solve this issue, for example, a shock absorbing material or the like is installed that suppresses the flow velocity of air in the bass reflex port.
However, in the case of using a structure that adds roundness in a radial shape to the angle of the opening ends a bass reflex port having a structure that extends the opening end three dimensionally and in a radial shape, since the linearity of the discharge air flow is strong, when being discharged, the air, while dispersing gradually, flows nearly straight ahead along the central axis of the bass reflex port, and is discharged with its flow velocity mostly maintained. Accordingly, if a grill is installed as described above, noise is produced. Moreover, the same phenomenon also occurs at the opening end on the side of the speaker unit. That is, noise is produced inside the enclosure by the air that is discharged from this opening end colliding with the speaker unit or an inner wall of the enclosure.
Also, in the case of a shock absorbing material being installed in the bass reflex port, the effect of bass enhancement diminishes since braking caused by air resistance from the shock absorbing material acts on the above-mentioned resonance action. The diminishing of the bass enhancement effect becomes prominent when the inner diameter of the bass reflex port must be narrowed to increase the flow velocity in order to make the enclosure compact.
Furthermore, when it is necessary to make a bend midway in the bass reflex port in order to increase the length of the bass reflex port, if the flow velocity of the bass reflex port is fast, the bend portion must be made into a shape that curves as gradually as possible. Accordingly, in this case structural restrictions are significantly incurred.